At the epitaxial growing stage of semiconductor crystal by using halogenide (practically chloride), Ga atoms, Si atoms, etc. are supplied to a substrate under growth in the form of chloride molecules such as GaCl, SiCl.sub.2, etc. and adsorbed to the surface of the substrate. Even after the adsorption of Ga, Si, etc., Cl atoms are left on the substrate, so that epitaxial growth of semiconductor crystal is not followed thereon, unless the Cl atoms are removed therefrom.
In a first conventional method for removing Cl atoms from an epitaxial growth surface, H.sub.2 molecules of carrier gas for supplying chloride molecules on a substrate under growth are reacted with the Cl atoms to form HCl molecules which leave the growth surface.
In a second conventional method for removing Cl atoms from an epitaxial growth surface, H atom radicals which are formed by the plasma decomposition of H.sub.2 molecules are used to remove Cl atoms from the epitaxial growth surface.
In the first conventional method, an activation energy as large as 40 to 50 kcal/mol is required to complete the HCl formation-reaction, when H.sub.2 molecules are used to remove Cl atoms, because the reaction is endothermical. The activation energy is based on a translation energy of H.sub.2 molecules which is determined by a temperature of a growth reaction chamber. For this reason, it is required that a temperature higher than a temperature for obtaining the surface adsorption of chloride molecules is set to promote the removal of Cl atoms. In a epitaxial growth method such as an atomic layer epitaxy, it is important that a temperature is set to be as low as possible to obtain a high control property.
In accordance with these aspects, there is a disadvantage in that a control precision inherent in the saturated-adsorption condition of chloride molecules can not be maintained, because a temperature can not be low in the removal of Cl atoms for the above described reasons. In addition, there is a further disadvantage in that a total crystal growth time is difficult to be shortened, unless the HCl formation reaction between H.sub.2 molecules and surface Cl atoms is accelerated, because the removal reaction is at rate-determining step in one cycle for the surface growth.
In the second conventional method by using H radical, the removal of Cl atoms can be carried out without the restriction of temperature. However, there is a disadvantage in that undesired result such as etching on the surface is observed due to the high reactivity of H atom radicals.